Work is said to be done when a force is applied, even if the object does not move. Class 9

Work is said to be done when a force is applied, even if the object does not move. Class 9

Revise, Reflect, Refine (Page 136-137)

Question 1.

State whether True or False. Class 9

(i) Work is said to be done when a force is applied, even if the object does not move.

Answer:

False. Work = Force x Displacement. If the object does not move (s = 0), work done = 0, regardless of the force applied.

(ii) Lifting a bucket vertically upward results in positive work done on the bucket.

Answer:

True. The applied force is upward and the displacement is also upward (same direction). Hence work done = F x s = positive.

(iii) The SI unit for both work and energy is joule (J).

Answer:

True. The SI unit of work is joule (J) = 1 N × 1 m. Energy has the same unit as work - joule (J).

(iv) A motionless stretched rubber band has kinetic energy.

Answer:

False. A motionless stretched rubber band has elastic potential energy (stored due to deformation), NOT kinetic energy. Since the band is stationary (v = 0), K = 1/2 mv² = 0.

(v) Energy can change from one form to another.

Answer:

True. Energy can and does convert from one form to another: electrical energy → light (bulb), chemical energy → mechanical energy (muscles), etc.